Continuity mistake: When the fat guys arrive at Peter's group, pay attention to the Asian guy in the first seat third row. After they open snacks he has switched seats with the other guy in the first seat second row. The guy he swapped seats with hair also changes color. (00:12:40)
Brian Goes Back to College - S4-E15
Continuity mistake: Brian stands outside of the gates of Brown University. The girl entering next to him has a backpack with a top flap that changes from brown to yellow and back. (00:08:05)
Petergeist - S4-E26
Continuity mistake: The table with the TV on in Peter and Lois' room is just a small table at the beginning of the episode when Stewie talks to the poltergeist. But as they speak to Stewie in the TV it's on a high up chest of drawers. (00:08:00 - 00:12:00)
Continuity mistake: On the tour bus, in one shot we see Meg wearing her outfit that she wore when she had her make-over. Then about 10 seconds later you see her in a different outfit altogether.
You May Now Kiss The...Uh...Guy Who Receives - S4-E25
Continuity mistake: When Peter drives his car in the field it is perfectly visible, but in the next couple of shots the car's gone, and so are the tire tracks.
The Courtship of Stewie's Father - S4-E16
Continuity mistake: After Peter and Stewie's Jungle Cruise ride, when Michael Eisner walks up to the duo, Eisner's suit buttons are on his left, but then the buttons switch to the opposite side, and his tie's stripes change direction as well. (00:19:50)
The Courtship of Stewie's Father - S4-E16
Continuity mistake: When Peter takes the garden hose upstairs, the bathroom doorknob is on the right side. As Peter kicks in the door, but from inside the bathroom, the doorknob is on the opposite side of the door, so it swings open the opposite way. (00:10:25)
The Courtship of Stewie's Father - S4-E16
Continuity mistake: After Peter's mess of glee club, in the first shot of Obi-Wan the right side of his robe is over his left side, but next shot it's the opposite way with the left side over the right. (00:02:15)
Brian Goes Back to College - S4-E15
Continuity mistake: After painting the stripe on the van, the side passenger door handle vanishes when Peter/Hannibal gets into the front seat; then, that handle reappears when Quagmire/Face enters the van. (00:09:10)
Brian Goes Back to College - S4-E15
Continuity mistake: When Brian is escorted into the New Yorker's writers' lounge, the door has a knob and backplate, but the backplate vanishes in a following shot. (00:03:15)
Brian Goes Back to College - S4-E15
Continuity mistake: After the opening credits, Peter/Hannibal is wearing a jacket with pockets only on his right side; then pockets suddenly appear on his left side between shots. (00:00:40)
Continuity mistake: Lois' breasts grow in size when Peter is trying to get Quagmire to snap out of his trance.
Brian Goes Back to College - S4-E15
Continuity mistake: When Brian arrives at Brown, his bag strap is across his body. When the shot changes, it's just on one shoulder. (00:08:00)
Brian Goes Back to College - S4-E15
Continuity mistake: Louis' hand changes places on the newspaper at the start when talking to Brian. Note its position in relation to the column. (00:02:10)
The Cleveland-Loretta Quagmire - S4-E5
Continuity mistake: When everyone starts playing charades, Joe is acting out a character. He has black shoes on. The boat throws him overboard and when back on the boat his shoes are white.
Continuity mistake: Brian and Stewie see Meg enter Mayor West's motel room. She's wearing a purple dress. They follow them to a restaurant and Meg has her regular hat and outfit on.
Petergeist - S4-E26
Continuity mistake: Lois slaps the skull out of Peter's hand and it lands on top of the dirt pile. They both turn around to look at the house and the skull is nowhere in sight.
Continuity mistake: At the start of the episode there's no coffee table beside the couch. When Brian is trying to prove to Peter that he has gravitational pull because of his weight, there's now a table with a bowl of fruit and a book.
Petergeist - S4-E26
Continuity mistake: The filing cabinet that was beside the TV moves to the corner beside the desk.